Not to be cynical, because I don't necessarily think there is a "right" answer for this particular application, but I don't see a huge advantage in doing this o

Not to be cynical, because I don't necessarily think there is a "right" answer for this particular application, but I don't see a huge advantage in doing this over a simple registration form with a password. An email is a unique field anyway, so when you say that "nobody likes creating a new username and password for a website" you are making the process sound more complicated than it really is. For the case of this site, the only difference is whether or not a password is required to log in. Additionally, should you want to add user-specific functionality later that persists across sessions, you will have to add an authentication system. Again, that's not to say that this method is right or wrong, but I myself have started down the road of maintaining sessions with cookies instead of full-blown authentication, and every time I have ended up going back to authentication because I always end up deciding that the benefits outweigh the drawbacks.